docs: def find_record(self, collection_name, query):
          """
          Return the first record mathing the given Mongo query.
  
          :param collection_name: Name of the collection to search in.
          :param query: MongoDB Query, e.g. {_id: 123}
          :return: A single MongoDB record or None if not found.
  
          :raise DataSourceError
          """
          cursor = self._get_collection(collection_name).find(query)
          for record in cursor:
              # Return the first record found.
              return record
          # Return None if nothing found.
          return None